July 2014 

NASA/TM–2014-218289 

Investigating Delamination Migration in 

Composite Tape Laminates 

James G. Ratcliffe 

Langley Research Center, Hampton, Virginia 

Nelson V. De Carvalho 

National Institute of Aerospace, Hampton, Virginia 
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July 2014 

NASA/TM–2014-218289 

Investigating Delamination Migration in 

Composite Tape Laminates 

James G. Ratcliffe 

Langley Research Center, Hampton, Virginia 

Nelson V. De Carvalho 

National Institute of Aerospace, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

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and Space Administration.
1

Abstract

A modification to a recently developed test specimen designed to investigate migration of a 

delamination between neighboring ply interfaces in tape laminates is presented. The specimen 

is a cross-ply laminated beam consisting of 40 plies with a polytetrafluoroethylene insert

spanning part way along its length. The insert is located between a lower 0-degree ply 

(specimen length direction) and a stack of four 90-degree plies (specimen width direction). The 

modification involved a stacking sequence that promotes stable delamination growth prior to

migration, and included a relocation of the insert from the specimen midplane to the interface 

between plies 14 and 15. Specimens were clamped at both ends onto a rigid baseplate and 

loaded on their upper surface via a piano hinge assembly, resulting in a predominantly flexural 

loading condition. Tests were conducted with the load-application point positioned at various 

locations along a specimen’s span. This position affected the sequence of damage events 

during a test. Delamination growth occurred prior to migration in specimens loaded at a location 

near to and ahead of the insert front. Conversely, delamination migration occurred first in 

specimens loaded at a position further behind the insert front. In the former cases, variation of 

the load-application location was found to affect the distance relative to this point at which 

migration initiated. Migration initiated in each specimen by a gradual transition of the 

delamination at the 0/90 interface into the 90-degree ply stack. In contrast, transition into the 

new 90/0 interface was sudden. A delamination resistance mechanism was observed that arose 

from delamination actually delving slightly into the lower 0-degree ply prior to migration. This 

implies that such an effect may be present during delamination at a non-unidirectional ply 

interface in any laminates subjected to flexural loading.

Introduction

Delamination is a failure mode commonly associated with composite tape laminates, and 

has thus received considerable attention focused on delamination as an individual mode of 

failure. For instance, considerable effort has been paid toward characterizing individual 

delamination, driven under mode-I, mode-II, mode-III and a mixture of these loading conditions 

[1-4]. Meanwhile, analysis methods have been developed that simulate delamination onset and 

growth along one ply interface without the possibility for migration of that delamination to 

another interface [5, 6]. While such analyses are adequate in many situations, delamination 

growth in laminates commonly involves migration between different ply interfaces [7-10]. 

Methods are being developed within the finite element analysis framework that enable 

simulation of such migration events [11, 12]. Experimental work has also focused on 

investigating delamination migration in laminates and utilized tests that involve multiple 

migration events [9, 13]. More recently, a test method was developed that was designed to 

characterize delamination migration and provide benchmarking data for validation of analyses 

for simulating migration [14]. This test specimen, depicted in Fig. 1, is a cross-ply laminate with 

a mid-plane insert spanning part way along the specimen length. The specimen is loaded to first 

cause onset of delamination growth from the insert front followed by migration of this 

delamination to another ply interface within the specimen. Overall, the delamination growth and 

migration events occur uniformly across the specimen width and thus the test yields data 

against which 2-dimensional analyses could be validated. One issue with the test is that 
2

delamination growth onset and migration tend to be unstable events, which makes simulating 

the test for validation purposes more cumbersome. The purpose of the work described here was 

to modify the stacking sequence of this delamination migration test specimen in order to 

promote stable delamination growth and migration. To this end, a series of analyses were 

conducted in order to determine an appropriate specimen stacking sequence. Specimens were 

manufactured, tested and examined for documentation of delamination migration.

Delamination Migration Tests

Specimen Configuration

The delamination migration test configuration is illustrated in Fig. 1 and is identical to that 

introduced recently [14]. The specimen possesses three main features that permit the controlled 

observation of delamination growth followed by a single migration event to another ply interface. 

First, the specimen is a cross-ply beam that yields uniform delamination growth and migration 

across the specimen width, such that observations from the specimen edges provide a good 

indication of fracture taking place through the specimen width. Second, the specimen contains a 

PTFE insert (acting as an artificial delamination) at an interface between a 0-degree ply 

(specimen span direction) and a stack of four 90-degree plies (specimen width direction). The 

0-degree ply acts to confine the delamination to this 0/90 interface by preventing the 

delamination from migrating through this ply. The 90-degree ply stack provides a path for the 

delamination to kink in to, leading to eventual migration. Third, the specimen can be loaded in a 

manner to cause delamination growth from the PTFE insert that eventually migrates to another 

ply interface. This sequence of fracture events is made possible by the way in which specimen 

loading affects shear stresses acting across the delamination front, in a manner described 

previously by Greenhalgh et al [15]. This process is illustrated in Fig. 2. In the case of the 

loading configuration illustrated in Fig. 2a (delamination front to the left of the load-application 

point), the shear stress acting across the PTFE insert front promotes kinking of the delamination 

towards the baseplate side of the specimen. However, the 0-degree ply below the PTFE insert 

prevents this from occurring, and instead, delamination grows along the 0/90 ply interface. The 

delamination continues to propagate along the 0/90 interface and grows past the loadapplication point (Fig. 2b), eventually leading to a reversal of the sign of the shear stress acting 

across the delamination front. The shear stress now promotes kinking of the delamination into 

the 90-degree ply stack towards the loaded side of the specimen, leading to complete migration 

of the delamination. More specific details regarding this migration process as it pertains to the 

current specimen can be found in [14].

Materials and Specimen Stacking Sequence

The composite material selected for this investigation was a IM7/8552 carbon/epoxy tape 

pre-preg manufactured by Hexcel [16]. In the current work, the specimen stacking sequence 

utilized for the original migration specimens [14] was modified to promote stable delamination 

growth onset and propagation. Hence, migration should be relatively more discernable from the 

specimen response, unlike migration in the original specimens, which took place during an 

unstable event where delamination growth also occurred [14].

Alternative stacking sequences for the migration specimen were evaluated by conducting 

2-dimensional finite element analyses of the specimen. The dimensions of the specimen 
3

considered in the analyses are given in Fig 1. The analyses were almost identical to those 

described in Ref. 14 (details of the finite element mesh, loading and boundary conditions are 

given in [14]). In the original migration specimens, the pre-implanted PTFE insert was located at 

the specimen mid-plane. Different positions within the specimen were considered in the current 

work on the hypothesis that shifting the insert away from the specimen mid plane may help to 

stabilize delamination growth. Four different load-application point positions (dimension, L, in 

Fig. 1) were considered. These locations corresponded to those examined experimentally in 

previous migration tests [14]. The four positions were as follows: L=a0, 1.1a0, 1.2a0 and 1.3a0, 

where the dimension, a0, is the length of the PTFE insert as illustrated in Fig. 1. A set of different 

delamination lengths (beginning with a length of a0) were considered for each loading position in 

order to manually represent delamination growth. The same prescribed displacement (z=1mm, 

Fig.1) was used in each analysis in order to emulate the displacement controlled loading under 

which the actual migration tests were conducted.

Upon completion of each analysis, the virtual crack closure technique (VCCT) [5] was utilized to 

compute the energy release rate GT (and its components GI and GII) for a set of fixed 

delamination lengths. Following [17], the critical load and displacement for each delamination 

length was obtained by linearly scaling the prescribed displacements and load:

where critical energy release rate, Gc, was assumed to be given by a mixed mode exponential 

law [17]. The resultant critical load-displacement curve was then used to assess the stability of 

each candidate layup, under displacement-control conditions. Additionally, for each stacking 

sequence, the specimen bending-twist coupling and the specimen’s ability to withstand the 

expected load levels were also assessed. 

The final stacking sequence chosen for the current specimens based on results from the 

above finite element analyses is shown in Fig. 3a. For comparison, the original stacking 

sequence [14] is shown in Fig. 3b. The overall number of plies in the current stacking sequence 

is the same as that in the original specimens. The main difference between the two stacking 

sequences is the location of the pre-implanted PFTE insert, which has been moved from the 

mid-plane down towards the lower portion of the specimen. The plies bounding the delamination 

(a lower 0-degree ply and an upper stack of four 90-degree plies) are the same as in the original 

specimen. The delamination is now located between ply 14 and 15 of the 44-ply laminate (ply 

#1 beginning from the bottom of the specimen as depicted in Fig. 3a).

An example result from a finite element analysis of a specimen with the new stacking sequence 

and loading position, L=1.1a0, is shown in Fig. 4, which is a plot of applied load, P versus loadpoint displacement, δ. The plot compares the critical load-displacement responses of a 

specimen with the original (OR) [14] and with the redesigned stacking sequence (S0). For the 

case considered in Fig. 4, the original stacking sequence shows unstable delamination growth 

under displacement-controlled conditions. This finding is in agreement with delamination growth 

observed in actual specimens [14]. Conversely, the redesigned layup shows stable delamination 

under displacement-controlled loading, as intended. Complementary analysis also showed that 

the extension-bending coupling of the redesigned layup was of the same order of magnitude as 

of the original layup [14], and that it was capable of withstanding the expected load range, 

confirming its suitability for testing. 

Pcrit = P Gc

GT

, δcrit = δ Gc

GT

(1)
4

Tests performed on actual migration specimens with the stacking sequence selected as a 

result of the current study confirmed that delamination growth in these specimens is mostly 

stable. Details of these tests are presented next.

Delamination Migration Tests

Specimens were loaded with 6 nominal loading positions: L=0.5a0, 0.8a0, a0, 1.1a0, 1.2a0, 

and 1.3a0 (where a0=48mm). Four repeat specimens of each load position were tested, 

resulting in a total of 24 specimens.

The migration tests were conducted using a servo-hydraulic test machine equipped with a 

22,250N load cell whose range was scaled to 2225N. Specimens were secured into the loading 

fixture pictured in Fig. 5. Specimens were clamped at both ends and loaded via a piano hinge 

bonded to the upper surface of the specimen. Precise details of the test fixture can be found in 

[14]. After proper alignment was established with the specimen length perpendicular to the 

hinge axis, specimens were loaded under displacement control at a rate of 0.127mm/min in the 

direction indicated in Fig. 1. Specimens were unloaded at the same loading rate. Applied load 

and crosshead displacement (referred to as displacement in the remainder of the paper) were 

recorded throughout each test. Delamination growth and migration was recorded by viewing 

both sides of each specimen using a pair of cameras equipped with macro lenses. Images of 

the delamination and migration events were recorded as they occurred during a test. The 

cameras were synchronized with the force and displacement output collected by the data 

acquisition system, enabling documentation of the exact force and displacement associated with 

each image.

Post-Test Inspection

The delamination and migration paths as viewed from both edges were inspected using an 

optical microscope at a 40-80X-magnification level. A selection of specimens tested with each 

loading position was inspected using X-ray computed tomography in order to gain an 

understanding of the fracture mechanisms within the body of the specimens. Specimens were 

also sectioned along the z-y plane (see coordinate system in Fig. 1) and examined under an 

optical microscope at a 40X-160X-magnification level. In addition, specimens were split along 

the existing delamination plane in order to confirm the PTFE insert front location.

Results/Discussion

Specimen Response

The applied load versus load-point displacement of a single specimen tested at each of the 

six loading points is shown in Fig. 6. The four repeat specimens of each load position exhibited 

consistent responses and thus a single case is shown in Fig. 6 to aid the comparison between 

the six cases. All specimens exhibited linear loading and unloading responses. In all cases, 

except for a loading position, L, equal to 0.5a0, delamination growth took place prior to 

migration. Generally, the distance from the load application point at which migration initiated, 

Dk, (see Figs. 7-12) decreased with increasing load position. The distance ranged from 

approximately 13mm at L=1.3a0, to 16mm at L=0.85a0. These findings are generally consistent 

with previous tests [14] and are discussed in more detail in the next section. Delamination 

growth onset was moderately unstable in all cases and was proceeded by mostly stable 
5

propagation until migration occurred, which was usually signified by a sudden load drop as 

indicated in Fig. 6. The specimens with a loading position, L=0.5a0 exhibited delamination 

migration immediately from the PFTE film insert. This was expected given that the shear 

stresses acting in the vicinity of the insert front tend to favor kinking of the delamination into the 

upper 90-degree ply stack. Migration initiated in these specimens at around 73% of the peak 

load. This was indicated by a very slight drop in load (at approximately 80N in the example 

shown in Fig. 6). Migration was eventually completed upon further loading, indicated by a small 

load drop (at approximately 110N in the example shown in Fig. 6). Sample load-displacement 

responses from each of the six load positions are given in Figs. 7-12 and include specimen 

edge views at key stages of each test (note, that the same force-displacement data shown in 

Fig. 6 are shown in Figs. 7-12).

A comparison of the load-displacement responses of the current specimens with responses 

of the original specimens [14] for load positions, L=a0, 1.1a0 and L=1.2a0, 1.3a0 is presented in 

Figs. 13 and 14, respectively. The comparison shows that delamination growth in the current 

specimens is relatively more stable than in the original specimens rendering migration generally 

more discernable from the response of the current specimens. For instance, in Fig. 13, the 

sudden load drop of the original specimen [14] (loading position, L=1.1a0) involved around 

15mm of delamination and migration. By contrast, delamination propagation (around 14mm of 

growth) in the current specimen with the same load position took place in a relatively stable 

manner prior to migration. Thus, specimens with the alternative stacking sequence satisfy the 

first objective of the current work, which was to encourage stable delamination propagation. 

However, the final unstable event that was typically exhibited by all specimens (that exhibited 

delamination prior to migration) involved around 1-3mm of delamination growth in addition to the 

migration event. Therefore the actual moment of migration is not exactly discernable from the 

specimen load-displacement response except for specimens that migrated immediately from the 

PTFE film insert. In specimens where delamination propagation occurred prior to migration (all 

load positions except L=0.5a0), specimen loading tends to increase (after initial delamination 

growth onset) as delamination propagation takes place. This effect was not anticipated from the 

finite element analyses conducted to evaluate candidate stacking sequences. For instance, with 

the new stacking sequence and load position, L=1.1a0, the applied load was predicted to 

decrease as delamination propagation takes place prior to migration (response of S0 in Fig. 4). 

Although initial delamination growth is accompanied by a gradual reduction in load during actual 

tests with this load position (L=1.1a0 in Figs. 6 and 13), the load eventually begins to increase 

upon further delamination until the instance of migration. In this example, the load at 

delamination growth onset is approximately 210N and the load increases to 260N at the point of 

migration after 20mm of delamination propagation. A similar behavior was observed in all other 

specimens (except for specimens with the load position, L=0.5a0). 

In the analysis, Gc was computed as a function of the mixed mode ratio, using an 

exponential law [17]. Gc for delamination onset and growth were assumed to be the same. 

Therefore, the increase in load observed experimentally, and not predicted in the analysis, 

suggests an increase in Gc with delamination growth.

The investigation of this apparent increase in resistance with delamination growth is 

presented in later in the section entitled, Nature of Delamination Growth and Migration.

Effect of Load Position on Migration

The plot in Fig. 15 shows the distance from the load-application point at which delamination 

migration onset was observed (Δk) as a function of normalized load position, L/a0. Each data 

point represents an average of four repeat tests. Although the scatter in these data between

repeat specimens at a given load position is moderately high (standard deviations ranged 

between 1 and 3mm), the overall data tend to show that migration onset occurs closer to the 

load-application point as the load position increases. Corresponding data from the previous 
6

migration tests [14] are included in Fig. 15 for comparison and exhibit a similar trend to the 

current data (at least for L/ a0>1). A previous explanation for this trend was that the load position 

affects the mixed-mode loading condition driving delamination growth, ultimately altering the 

location at which migration takes place. Migration, however, took place slightly further from the 

load-application point in the current specimens, which is most likely due to the differing stacking 

sequence of the current specimens versus those tested previously [14].

A plot of kink angle, Ω, (see Fig. 2b) as a function of load position is also included in Fig. 15. 

Each data point represents an average from four repeat specimens at each load position. 

Corresponding data from the previous migration tests [14] are also included in the figure and 

show that kink angle in the current specimens is similar to that in previous specimens for a 

given load position. Kink angles in the current specimens generally reduced with load position, 

decreasing from 72 degrees at L≈0.5a0 to 49 degrees at L=1.3a0. Scatter in the current kink 

angle data was moderate with a maximum standard deviation of 11 degrees in the data 

corresponding to the load position, L=1.3a0.

Nature of Delamination Growth and Migration

As discussed at the beginning of this section, a mechanism was observed that appears to 

resist delamination growth in the current specimens. This is manifested in a general increase in 

applied load as delamination occurs (as shown in Fig. 6). This mechanism was unexpected on 

the basis of the design analysis results, which predicted a general decrease in applied load with 

continuing delamination growth. In order to understand this resistance phenomenon, specimen 

delamination surfaces were examined using X-ray computed tomography. Following these X-ray 

inspections, specimens were sectioned and polished in order to reveal the location of 

delamination and migration with respect to the specimen plies local to these features.

Images of the upper delamination surface of a specimen from each of the six load positions, 

taken using X-ray computed tomography, are presented in Fig. 16 (the upper surface being that 

indicated in Fig. 3). The dark, horizontal bands that appear near to the bottom of each image 

correspond to the crack that kinked through the upper 90-degree ply stack resulting in migration. 

The specimen with a load position, L=0.5a0, exhibited migration immediately from the PTFE 

film insert. In all other cases a certain amount of delamination growth took place prior to the final 

migration event. The delamination surface in all these cases exhibits two common features. 

First, imprints of 0-degree fibers are apparent on the delamination surface and tend to transition 

into finger-like patterns up to the kinked crack region. Second, horizontal lines appear along the 

delamination surface part way towards the migration region. X-ray inspection confirmed that 

these lines are in fact cracks that kinked part or all the way through the upper stack of four 90-

degree plies. 

The imprints of the 0-degree fibers indicate that delamination growth partly dives under the 

surface of the bounding 0-degree ply during initial stages of delamination growth (typically 

before it has reached the load-application point). Specimens tested with each load position were 

also sectioned and the exposed surfaces polished in order to further explore where

delamination took place prior to migration. Of the specimens that exhibited delamination prior to 

migration, the overall features were very similar. Images of polished sections of a specimen with 

a load position, L=1.1a0, are presented in Fig. 17 and are from the same specimen of which an

X-ray image is presented in Fig. 16. First, one of the specimen edges was polished and three 

images (labeled 1-3 in Fig. 17) were taken along the path of delamination growth beginning from 

the PTFE film insert-front region and ending at the migration (this edge corresponds to the lefthand side of the X-ray image of this specimen’s delamination surface in Fig. 16). The images 

indicate that delamination growth from the insert front took place near to the 0/90 ply interface, 

which transitioned into the lower 0-degree ply upon further growth up to the moment of 

migration. The X-ray imaging also indicated that the extent with which delamination took place 

within the 0-degree ply varied along specimen width, therefore specimens were sectioned at the 
7

locations shown in Fig. 17 (labeled Section AA and Section BB) in order to help further establish 

the location of delamination growth. Three images were taken at each section, the first (lefthand side) corresponding to the edge shown in images 1-3, the second (middle) corresponding 

to the specimen mid-width, and the third image (right-hand side) corresponding to the other 

edge of the specimen. The images generally confirm what was suspected from the previous 

observations: that delamination tends to remain near the 0/90 ply interface at the beginning of 

delamination growth, eventually transitioning just into the 0-degree ply (with the extent of this 

transition varying across the width). This delving of the delamination into the 0-degree ply 

causes some fibers to bridge the delamination, and therefore causes additional resistance to the 

delamination growth. This mechanism, referred to herein as ply delving, is thought to be an 

analogue to fiber bridging observed in characterization specimens such as the double cantilever 

beam specimen [18, 19]. This ply delving is thought to occur because of misalignment of fibers 

in the bounding 0-degree ply, which create paths for the delamination to propagate into the ply 

during the initial stages of growth when local shear stresses tend to kink the delamination 

towards this ply (see Fig. 2a). Furthermore, evidence of this ply delving near the mid-width 

region of the specimens (middle image of Section BB in Fig. 17) also implies that this is not 

simply an artifact of free-edge effects in the specimens.

After a certain amount of delamination growth (note, always after the delamination has 

propagated past the load application point), the shear stress changes sign, promoting kinking of 

the delamination up into the 90-degree ply stack. Notably, the kinked cracks that are evident 

prior to final delamination migration, Fig. 16, do not extend across the entire specimen width. As 

noted previously, the extent of ply delving into the bounding 0-degree ply varies across the 

width of the present specimens. In places where a lesser amount of delving has taken place, the 

delamination local to these regions begins kinking into the 90-degree ply stack (resulting in the 

horizontal lines in Fig. 16). However, more ply delving is evident in other positions across the 

specimen width, which helps to prevent kinking even when the local stress state makes this 

feasible. At this stage of delamination growth, the local shear stresses, which would now tend to 

kink the delamination through the 90-degree ply stack, are prevented from doing so by the 

bridging fibers that resulted from the ply delving. This is thought to essentially delay the moment 

at which migration occurs, which will do so once the propagating delamination is able to 

meander through the 0-degree ply up into the 90-degree ply stack. This mechanism is thought 

to be the reason for the finger-like patterns up to the region of migration evident in the X-ray 

images in Fig. 16.

Beyond confirming the nature of delamination growth in the present specimens, these 

findings offer possibly more general insight into the nature of delamination (driven by flexural 

loading such as that during a low-velocity impact event) in a laminate growing at a nonunidirectional ply interface. First, the current findings suggest that delamination growth will 

generally follow the fiber direction of the ply whose fibers can largely oppose the tendency of the 

delamination to otherwise kink through the ply (resulting in would-be migration). Second, once 

this so-called bounding ply facilitates delamination growth, inherent misalignment of fibers in this 

ply may result in the resistance effect resulting from the ply delving mechanism observed in the 

present specimens. A possible implication of these considerations is that some form of 

delamination resistance effect may often be present during delamination created under flexural 

loading at a multi-unidirectional ply interface. If this implication turns out to be true and is a 

significant effect, it should be included during simulations of delamination at non-unidirectional 

ply interfaces. This situation raises the question of how to characterize such a resistance effect 

for inclusion in an analysis. Of course, this effect may well be exclusive to the present 

specimens owing to the almost purely flexural load application and the unconventional stacking 

sequence utilized. However, this is yet to be confirmed and may serve as a useful focal point for 

a future study.
8

Concluding Remarks

A stacking sequence was identified that promotes stable delamination growth onset and 

migration in the delamination migration test specimen. Specimen responses were documented 

and the nature of delamination growth and migration was investigated. Generally, the position of 

the load-application point had a mild effect on the location along the length of a specimen in 

which migration took place. Closer examination of delamination prior to migration via X-ray 

computed tomography and optical inspection revealed that delamination tends to delve into the 

surface of the bounding 0-degree ply until the point of migration. Further examination suggested 

that this ply delving phenomenon was likely responsible for the delamination resistance effect 

observed in all specimens that exhibited delamination prior to the migration event. A possible 

implication of these observations is that some form of delamination resistance effect may often 

be present during delamination at a non-unidirectional ply interface in a laminate subjected to 

flexural loading. Hence, it may be necessary to include this resistance effect during simulations 

of delamination at non-unidirectional ply interfaces. Further study is required to determine how 

to best characterize such a resistance effect for inclusion in an analysis.

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9

[12] D.L. Yang and B. Cox “An Augmented Finite Element Method for Modeling Arbitrary 

Discontinuities in Composite Materials,” International Journal of Fracture, Vol. 156, No. 1, 

pp 53-73, 2009.

[13] C. Canturri, E.S. Greenhalgh, S.T. Pinho and J. Ankersen. “Delamination Growth 

Directionality and the Subsequent Migration Processes – The Key to Damage Tolerant 

Design,” Presented at the 15th European Conference on Composite Materials, Venice, 

Italy, 24-28 June, 2012.

[14] J. Ratcliffe, M. Czabaj and T.K. O’Brien “Characterizing Delamination Migration in 

Carbon/Epoxy Tape Laminates,” NASA Technical Memorandum, NASA-TM-2013-218028, 

August, 2013.

[15] Greenhalgh, E.S., C. Rogers, and P. Robinson. “Fractographic Observations on 

Delamination Growth and the Subsequent Migration Through the Laminate,” Composites 

Science and Technology, Vol. 69, pp.2345-2351, 2009.

[16] Hexcel Corporation. “HexPly® 8552 Product Data Sheet,” http://hexcel.com, 2007.

[17] R. Krueger “Development and application of benchmark examples for mixed –mode I/II

quasi-static delamination propagation predictions,” NASA/CR-2012-217562, 2012.

[18] “ASTM D 5528-13, Standard Test Method for Mode I Interlaminar Fracture Toughness of 

Unidirectional Fiber-Reinforced Polymer Matrix Composites,” in Annual Book of ASTM 

Standards. Vol. 15.03, American Society for Testing and Materials, 2014.

[19] W.S. Johnson and P.D. Mangalgari. “Investigation of Fiber Bridging in Double Cantilever 

Beam Specimens,” Journal of Composite Technology and Research, Vol 9, pp. 10–13, 

1987.
10

300.0

Clamp

Clamp

a0=48

12.7

12.7

L

S = 115 Baseplate

Specimen

[0]10

[90]4

[0]

[90]

[0]2

Applied 

load

0o h=5.29

2mm gap

All units in mm. Not drawn to scale

Specimen width (y-axis), 

B=12.7mm

90o-direction parallel to y-axis

Fig. 1. Schematic of delamination migration test configuration.

[0]10

[90]4

[0]

a/L > 1

a

a/L < 1

L

L

(a) a (b)

Ω 

Principal tensile 

stress plane

Principal tensile 

stress plane

Fig. 2. Shear stresses acting across the delamination front at different stages of 

growth.

[0]10

[90]4

[0]

Delamination tip
11

Fig. 4. Comparison between the critical load-displacement response of the original layup (OR) 

and of the redesigned layup (S0).

a"

L=1.1a" U"

0 

50 

100 

150 

200 

250 

300 

350 

0 0.5 1 1.5 

P 

[N] 

δ [mm] 

OR 

S0 

unstable 

region 

New stacking sequence and PTFE insert location:

[04/9012/010/904/ T/0/90/02/906/02/90/0]

Original stacking sequence and PTFE insert location:

[904/03/(90/0)2s/03/904/T/0/904/0/0/(90/0)2s/0/0/903/0/90]

Notes:

Sequence of plies: Left to right corresponds to upper to 

lower surfaces of the specimen.

PTFE insert location indicated by letter, T.

(a)

(b)

Upper delamination 

surface

Fig. 3. New versus original stacking sequences.
12

Fig. 5. Test fixture with loaded specimen.

Fig. 6. Load displacement responses of migration specimens.

Lower baseplate

Upper baseplate

Loading rod

Specimen

Camera

Piano hinge

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm]"

L=0.5a0

L=0.85a0

L=a0

L=1.1a0

L=1.2a0

L=1.3a0

78.50 

80.00 

1.24 1.27 

P 

[N] 

δ [mm] 
13

Fig. 7 Load-displacement response and fracture events: L=0.5a0.

Fig. 8 Load-displacement response and fracture events: L=0.85a0.

0 

20 

40 

60 

80 

100 

120 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=0.5a0 Δk≈25mm

0 

40 

80 

120 

160 

200 

240 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=0.85a0

Δk≈16mm

78.50 

80.00 

1.24 1.27 

P 

[N] 

δ [mm] 
14

Fig. 9 Load-displacement response and fracture events: L=a0.

Fig. 10 Load-displacement response and fracture events: L=1.1a0.

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=1.1a0

Δk≈13mm

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=a0 Δk≈15mm
15

Fig. 11 Load-displacement response and fracture events: L=1.2a0.

Fig. 12 Load-displacement response and fracture events: L=1.3a0.

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=1.2a0

Δk≈12.5mm

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=1.3a0 Δk≈12.7mm
16

Fig. 13. Load displacement response of current and original specimens (L=a0 and 1.1a0).

Fig. 14. Load displacement response of current and original specimens (L=1.2a0 and 1.3a0).

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 3 

P 

[N] 

δ [mm] 

Current specimens:

L=a0

Previous specimens [14]: L=1.1a0

L=a0

L=1.1a0

0 

80 

160 

240 

320 

400 

0 0.5 1 1.5 2 2.5 

P 

[N] 

δ [mm] 

L=a0

L=1.1a0

Current specimens

Previous specimens [14]:

L=a0

L=1.1a0
17

Fig. 15. Effect of load position on migration position and kink angle.

Current specimens

Previous specimens [14]

Current specimens

Previous specimens [14]
18

L=0.47a0 L=0.85a0 L=a0

L=1.10a0 L=01.20a0 L=1.30a0

Centerline of load-application point

PTFE film insert front

Migration

Migration

Fig. 16. X-ray computed tomography images of upper delamination surface.
19

L=1.1a0

1 2 3

A

A

B

B

2

1

3

Section A-A

Section B-B

Fig. 17. Optical images of section cuts from specimen with L=1.1a0.

0.5mm

0.5mm

0.5mm

0.5mm

0.5mm

0.5mm

0.5mm

0.5mm

0.5mm
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

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Technical Memorandum

 4. TITLE AND SUBTITLE

Investigating Delamination Migration in Composite Tape Laminates 

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Ratcliffe, James G.; De Carvalho, Nelson V.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

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 REPORT NUMBER

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NASA

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STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

A modification to a recently developed test specimen designed to investigate migration of a delamination between neighboring 

ply interfaces in tape laminates is presented. The specimen is a cross-ply laminated beam consisting of 40 plies with a 

polytetrafluoroethylene insert spanning part way along its length. The insert is located between a lower 0-degree ply (specimen

length direction) and a stack of four 90-degree plies (specimen width direction). The modification involved a stacking 

sequence that promotes stable delamination growth prior to migration, and included a relocation of the insert from the 

specimen midplane to the interface between plies 14 and 15. Specimens were clamped at both ends onto a rigid baseplate and 

loaded on their upper surface via a piano hinge assembly, resulting in a predominantly flexural loading condition. Tests were 

conducted with the load-application point positioned at various locations along a specimen’s span. This position affected the 

sequence of damage events during a test. 

15. SUBJECT TERMS

Delamination; Method; Migration; Test

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